For the vortex flow meter, a vortex generator is disposed perpendicularly to a flow direction of a fluid to be measured in a measurement pipe line, the Karman vortex is generated by the vortex generator, and a flow rate of the fluid to be measured is measured by detecting an alternating force acted by the Karman vortex that is applied to a forced member disposed at the downstream of the vortex generator in the pipe line.
Japanese Laid-Open Patent Publication No. 2000-321102 discloses the vortex flow meter in which a measurement pipe line, a vortex generator, and a forced member that come into contact with corrosive chemicals are all made of a fluorocarbon resin as a vortex flow meter that can measure a flow rate of the corrosive chemicals for cleaning in a semiconductor cleaning apparatus.
For a semiconductor cleaning apparatus in recent years, a case has become increased in which a high temperature cleaning solvent is used. In such a semiconductor cleaning apparatus, a flow meter becomes a high temperature state. More specifically, a typical usage condition in an SPM cleaning is cleaning for approximately ten minutes at a temperature in the range of 100 to 120° C. using the chemicals of H2SO4 (sulfuric acid):H2O2 (hydrogen peroxide)=4:1. Moreover, there is demanded a cleaning at a higher temperature in the range of 160 to 170° C. to enhance a cleaning performance.
However, in the case in which the above described vortex flow meter made of a fluorocarbon resin is used for such an apparatus performing a cleaning at a high temperature, there is a problem that a measurement error occurs due to a temperature change since a coefficient of linear thermal expansion of the fluorocarbon resin is large to a temperature and a cross sectional area of a measurement pipe line of the flow meter increases as compared to a normal temperature (20° C.).
More specifically, since a coefficient of linear thermal expansion of the fluorocarbon resin is 12×10−5° C.−1 at a temperature in the range of 20 to 100° C., a change in a cross sectional area of approximately 2% occurs at 20° C. and 100° C. and a measurement error occurs due to a temperature change. A flow rate is represented by the expression of Q=S×V (Q: flow rate, S: passage cross sectional area, V: flow velocity). In the case in which the passage cross sectional area S of a measurement pipe line increases due to a temperature change and the actual flow rate Qa is constant, the flow velocity V becomes lower, and the measured flow rate Qm is smaller than the actual flow rate Qa. Moreover, in the case in which a shape of the measurement pipe line changes due to a pressure and the passage cross sectional area S becomes larger, it is thought that a measurement error becomes larger.
A fluorocarbon resin makes corrosive chemicals to permeate according to a lapse of time, thereby causing parts of a circuit board to be corroded. Moreover, since a creep easily occurs to a fluorocarbon resin in the case in which a temperature of a fluid to be measured is high, chemicals easily leak from a sealed section for a vortex flow meter using a sealing member to seal a corrosive fluid, thereby corroding parts of a circuit board and causing a failure.
Moreover, depending on a usage environment, a mechanical vibration is applied to a vortex flow meter from surroundings, and a measurement error may occur due to the vibration.
The present invention was made in order to solve the above problems of the prior art. An object of the present invention is to provide a vortex flow meter with less measurement errors caused by a temperature change, a pressure change, and a mechanical vibration, and capable of performing a precise measurement regardless of conditions.
Another object of the present invention is to provide a vortex flow meter capable of sufficiently preventing corrosive chemicals that is a fluid to be measured from leaking from a measurement pipe line due to corrosion.